Conventionally, productivity of crops has been improved by carrying out breed improvement backed up with experience, by exterminating insects using agrichemicals, and by other methods. However, with a rapid development in molecular biology in recent years, a molecular breeding method (such as producing a transformed plant) makes it possible to develop crops having high productivity. Specific examples of techniques for improving productivity of crops encompass: promotion of growth (improvement in plant growth traits); addition of traits (i.e., pest controlling traits) for controlling the incidence caused by pests including insects and diseases; addition of stress resistance; addition of a dwarf character; control of flowering time; and the like. Beside the foregoing examples, there are various kinds of techniques leading to improvement in productivity either directly or indirectly.
The techniques directly leading to the improvement in the productivity include the promotion of plant growth (the improvement in the plant growth traits). For example, Non-Patent Document 1 reports that tobacco having overexpressed cyanobacterial fructose-1,6/sedoheptulose-1,7-bisphosphatase improves its plant growth traits. Non-Patent Document 2 discloses that Arabidopsis thaliana introducing Dof1 transcription factor improves its plant growth traits under low-nitrogen conditions.
Also, adding the pest controlling traits to crops improves productivity, compared with crops damaged by pests including insects and diseases. The techniques for producing a plant having the pest controlling traits by means of introducing a specific gene into a plant have been reported so far. For example, Patent Document 1 discloses such a method that transformation is carried out with a gene encoding a constitutively active form of G-protein α-subunit so as to produce rice improved in tolerance against bacterial leaf blight. Also, Patent Document 2 discloses that rice transformed with a gene encoding a defensin protein is resistive against rice blast and bacterial leaf blight.
In some cases, however, adding the pest controlling traits does not lead to improvement in productivity. For example, it is known that plant growth traits are diminished in a plant in a case where a gene related to stress resistance (including the pest controlling traits) is constitutively expressed in the plant (refer to Non-Patent Documents 3 to 5), and it is described that some kinds of efforts are necessary for the purpose of ensuring the plant growth traits.
[Patent Document 1]
    Japanese Unexamined Patent Application Publication, Tokukai, No. 2005-192496 (published on Jul. 21, 2005)[Patent Document 2]    Japanese Unexamined Patent Application Publication, Tokukai, No. 2003-88379 (published on Mar. 25, 2003)[Non-Patent Document 1]    Miyagawa Y, Tamoi M, Shigeoka S. Overexpression of a cyanobacterial fructose-1,6-/sedoheptulose-1,7-bisphosphatase in tobacco enhances photosynthesis and growth. Nat Biotechnol. 2001 October; 19(10): 965-9.[Non-Patent Document 2]    Yanagisawa S, Akiyama A, Kisaka H, Uchimiya H, Miwa T. Metabolic engineering with Dof1 transcription factor in plants: Improved nitrogen assimilation and growth under low-nitrogen conditions. Proc Natl Acad Sci USA. 2004 May 18; 101(20): 7833-8. Epub 2004 May 10.[Non-Patent Document 3]    Berrocal-Lobo M, Molina A, Solano R. (2002) Constitutive expression of ETHYLENE-RESPONSE-FACTOR1 in Arabidopsis confers resistance to several necrotrophic fungi. Plant J. 29: 23-32.[Non-Patent Document 4]    Kasuga M, Liu Q, Miura S, Yamaguchi-Shinozaki K, Shinozaki K. (1999) Improving plant drought, salt, and freezing tolerance by gene transfer of a single stress-inducible transcription factor. Nat Biotechnol. 17: 287-291.[Non-Patent Document 5]    Tang X, Xie M, Kim Y J, Zhou J, Klessig D F, Martin G B. (1999) Overexpression of Pto activates defense responses and confers broad resistance. Plant Cell. 11: 15-29.